Method and apparatus for transmitting and receiving variable rate data

ABSTRACT

A variable rate transmission system transmits a variable rate data packet including an accompanying rate indication signal indicative of the transmission rate of the variable data packet. The data packet can be spread using a long pseudonoise (PN) code, the mask of which can be selected in accordance with the transmission rate of the variable rate data packet. A preamble, providing the transmission rate, can be punctured into an outgoing pilot signal. The rate indication signal can be encoded in accordance with a set of orthogonal functions that are part of the indication of the transmission rate of the data packet.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for patent is a Continuation and claims priorityto patent application Ser. No. 10/858,873 entitled “METHOD AND APPARATUSFOR TRANSMITTING AND RECEIVING VARIABLE RATE DATA,” filed Jun. 1, 2004,now allowed; which is a Continuation and claims priority to patentapplication Ser. No. 09/158,254 entitled “METHOD AND APPARATUS FORTRANSMITTING AND RECEIVING VARIABLE RATE DATA,” filed Sep. 22, 1998, nowU.S. Pat. No. 6,798,736, issued on Sep. 28, 2004; both assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention relates to communications. More particularly, thepresent invention relates to a method and apparatus for transmitting andreceiving variable rate packets of data with signals indicative of thedata rate of those packets.

2. Background

The use of code division multiple access (CDMA) modulation techniques isone of several techniques for facilitating communications in which alarge number of system users are present. Although other techniques suchas time division multiple access (TDMA), frequency division multipleaccess (FDMA), and AM modulation schemes such as amplitude compandedsingle sideband (ACSSB) are known, CDMA has significant advantages overthese other techniques. The use of CDMA techniques in a multiple accesscommunication system is disclosed in U.S. Pat. No. 4,901,307, entitled“SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE ORTERRESTRIAL REPEATERS,” and assigned to the assignee of the presentinvention and incorporated by reference herein. The use of CDMAtechniques in a multiple access communication system is furtherdisclosed in U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FORGENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,”assigned to the assignee of the present invention and incorporated byreference herein.

In the aforementioned U.S. Pat. No. 5,103,459 (the '459 patent), the useof orthogonal Walsh codes to provide channelization to differentsubscriber stations is described. This allows a base station to transmitmany separate channels to a plurality of users in the coverage area ofthe base station. In the '459 patent, one of the orthogonal Walshchannels that was transmitted was a pilot channel that allowed for thecoherent demodulation of the traffic channels transmitted on otherorthogonal Walsh channels. A method for transmitting a CDMA signal froma mobile station which is capable of coherent demodulation is describedin U.S. patent application Ser. No. 08/856,428, now abandoned, entitled“REDUCED PEAK TO AVERAGE TRANSMIT POWER HIGH DATA RATE IN A CDMAWIRELESS COMMUNICATION SYSTEM,” filed May 14, 1997, assigned to theassignee of the present invention and incorporated by reference herein.In U.S. patent application Ser. No. 08/856,428, the mobile stationtransmits a plurality of different channels wherein each of the channelsis distinguished by use of a short Walsh sequence. In addition, U.S.patent application Ser. No. 08/856,428 describes a method of complexpseudonoise (PN) spreading that reduces peak to average ratio in thetransmission of a QPSK modulated signal.

CDMA systems often employ a variable rate vocoder to encode data so thatthe data rate can be varied from one data frame to another. An exemplaryembodiment of a variable rate vocoder is described in U.S. Pat. No.5,414,796, entitled “VARIABLE RATE VOCODER,” assigned to the assignee ofthe present invention and incorporated by reference herein. The use of avariable rate communications channel reduces mutual interference byeliminating unnecessary transmissions when there is no useful speech tobe transmitted.

Similarly, it is desirable for providing variable rate transmission ofdigital data in CDMA wireless communication systems. When there is agreat deal of digital information to be transmitted and when minimizingdelay is important, then data should be transmitted at high transmissionrates. However, when there is less data to be transmitted or whenminimizing delay is not as important, it is desirable to reduce thetransmission rate of digital data in a wireless communication system,because transmission at rates lower than the maximum transmission ratecan result in increased range, extended battery life and reduceinterference to other users.

One technique for the receiver to determine the rate of a received dataframe is described in U.S. Pat. No. 5,566,206, entitled “METHOD ANDAPPARATUS FOR DETERMINING DATA RATE OF TRANSMITTED VARIABLE RATE DATA INA COMMUNICATIONS RECEIVER,” assigned to the assignee of the presentinvention and incorporated by reference herein. Another technique isdescribed in U.S. patent application Ser. No. 08/126,477, entitled“MULTIRATE SERIAL VITERBI DECODER FOR CODE DIVISION MULTIPLE ACCESSSYSTEM APPLICATIONS,” filed Sep. 24, 1993, now U.S. Pat. No. 5,710,784,issued Jan. 20, 1998 to Kindred et al., assigned to the assignee of thepresent invention, and incorporated by reference herein. According tothese techniques, each received data frame is decoded at each of thepossible rates. Error metrics, which describe the quality of the decodedsymbols for each frame decoded at each rate, are provided to aprocessor. The error metrics may include Cyclic Redundancy Check (CRC)results, Yamamoto Quality Metrics, and Symbol Error Rates. These errormetrics are well-known in communications systems. The processor analyzesthe error metrics and determines the most probable rate at which theincoming symbols were transmitted.

SUMMARY

The present invention provides a novel and improved apparatus and methodfor transmitting and receiving variable rate data. In the firstembodiment of the present invention, the data is spread using a longpseudonoise code generated by a linear feedback PN generator, the maskof which is selected in accordance with the transmission rate of thevariable data and the specific user transmitting the data. Thus, byidentifying at the receiver which mask will allow the received waveformto be correctly despread, the rate of the data can be determined. In thesecond embodiment of the present invention a preamble from apredetermined set of preambles is punctured into the outgoing pilotsignal to provide rate indication information. In the third embodiment,the rate indication signal is encoded in accordance with a set oforthogonal functions which are part of the indication of the rate of thedata packet.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a block diagram of the transmission system of the firstembodiment of the present invention;

FIG. 2 is a block diagram of an exemplary PN generator;

FIG. 3 is a diagram illustrating the bits used for the long code mask;

FIG. 4 is a block diagram illustrating the first receiver system forreceiving variable rate data transmitted by means of the firstembodiment of the present invention;

FIG. 5 is a block diagram illustrating the second receiver system forreceiving variable rate data transmitted by means of the firstembodiment of the present invention;

FIG. 6 is a block diagram illustrating the transmitter system of thesecond embodiment of the present invention;

FIGS. 7A-7H are diagrams illustrating a proposed set of preamble formatsfor use in the second embodiment of the present invention;

FIG. 8 is a block diagram illustrating the receiver system of the secondembodiment of the present invention;

FIG. 9 is a block diagram of a remote station of the present inventionillustrating the transmitter system of the third embodiment of thepresent invention; and

FIG. 10 is a block diagram illustrating the receiver system of the thirdembodiment of the present invention.

DETAILED DESCRIPTION

Referring to the figures, FIG. 1 illustrates the transmission apparatusof the present invention in block diagram form. The data packet to betransmitted is provided to cyclic redundancy check (CRC) and tail bitgenerator 2. The number of bits of data in the data packet determinesthe effective rate R of the transmission. CRC and tail bit generator 2generates a set of CRC bits such as parity bits in accordance withmethods that are well known in the art. The CRC bits along with a set oftail bits are appended to the data packet.

The data packet with the appended CRC and tail bits is provided toforward error correction encoder 4. Encoder 4 can be any form of digitalforward error correction encoder, such as a convolutional encoder, aReed Solomon encoder or other known forward error correction coder. Inthe exemplary embodiment, encoder 4 is a turbo coder, the design ofwhich is well known in the art and is described in detail in U.S. Pat.No. 5,446,747, entitled “ERROR-CORRECTION CODING METHOD WITH AT LEASTTWO SYSTEMATIC CONVOLUTIONAL CODINGS IN PARALLEL, CORRESPONDINGITERATIVE DECODING METHOD, DECODING MODULE AND DECODER,” which isincorporated by reference herein.

The encoded packet is provided to interleaver 6 which reorders theencoded symbols in the packet to provide temporal diversity thatprovides for additional protection against burst errors. The reorderedpacket is then provided to repetition generator 8 which providesredundant versions of the interleaved symbols into the packet so as tooutput packets of fixed number of symbols regardless of the data rate ofthe packet R. The packet from repetition generator 8 is provided to gainelement 10 which adjusts the gain of the packet in accordance with therate R of the packet and in order to provide the correct power ratiobetween the pilot channel and the data channel.

The packet from gain element 10 is provided to subchannel spreadingelement 12. Subchannel spreading element 12 spreads the packet using ashort spreading sequence (W_(data)) that is used to allow the receiverto separate the pilot channel from the data channel. In the exemplaryembodiment, the short spreading sequences used are short orthogonalWalsh sequences. The use of short orthogonal Walsh sequences to providechannelization on the reverse link is described in detail in theaforementioned U.S. patent application Ser. No. 08/856,428, nowabandoned. The spread packet from subchannel modulation element 12 isprovided to scrambling element 18. Scrambling element 18 scrambles thepacket in accordance with a pseudonoise (PN) sequence generated by longcode generator 16.

Turning to FIG. 2, an exemplary embodiment of the PN generator 16 isillustrated. The packet is covered using a pseudonoise (PN) sequencederived from a IIR filter 50 composed of a linear shift register withassociated summing elements and taps. In the exemplary embodiment, IIRfilter 50 is a 42 tap IIR filter that is used in the scrambling ofreverse link transmissions in the Telecommunications IndustryAssociation standard TIA/EIA/IS-95-A, entitled “Mobile Station-BaseStation Compatibility Standard for Dual-Mode Wideband Spread SpectrumCellular System.”

The outputs from IIR filter 50 are provided to a bank of AND gates 52.Each of the outputs of IIR filter 50 is ANDed with a 42-bit Long CodeMask. The results of the ANDing operations are provided to modulo-2addition means 54, which performs the summing operation to provide thelong code sequence as a serial output. The long code generated in thisfashion has important autocorrelation characteristics that are wellknown in the art. Long codes of this fashion are used in cellular CDMAsystems to distinguish one mobile station from another. When twodistinct long code masks are used, the resulting two long code sequencesare uncorrelated or at least have very limited correlation. The presentinvention takes advantage of this property of the generated long codesin order to encode the rate information.

As shown in FIG. 3, in the present invention the exemplary 42-bit longcode mask comprises n bits which identify the rate of transmission and42-n bits, which are used to identify the user. For example, if thereare two possible transmission rates, then a single bit (n=1) would besufficient to identify the transmission rate. If there were 3 or 4possible transmission rates, then two bits (n=2) would be necessary tospecify the rate, and so on. In FIG. 3, the bits identifying thetransmission rate are the most significant bits (MSBs), however, any ofthe bits would be equally applicable, and the bits identifying the rateneed not even be consecutive.

Returning to FIG. 1, the information regarding the rate of theinformation is provided to mask selector 14 that provides a mask inaccordance with the rate information R and the identity of thetransmitting remote station. Mask selector 14 could be implemented usinga memory device such as a RAM or ROM device that stores mask codes thatare retrieved in accordance with the rate of the packet to betransmitted. The selected mask is provided to long code generator 16which provides the generated long code to scrambling elements 18 and 22.

In the exemplary embodiment, the remote station transmits both a datachannel and a pilot channel that allows for coherent demodulation of itstransmitted signal. The present invention is not limited to systems thattransmit a data channel with an accompanying pilot channel nor is itlimited to reverse link transmissions. The present invention is equallyapplicable to any variable rate transmission system in which thereceiver does not know a priori the rate of the transmission and inwhich the data is scrambled using a pseudonoise sequence.

A set of pilot signal bits is provided to subchannel spreading element20. The pilot signal carries no information, and the exemplaryembodiment is simply a string of zeroes. The pilot bits are spread by ashort Walsh sequence W_(pilot), which in the exemplary embodiment isorthogonal to W_(data), and is used to distinguish the pilot channelfrom the data channel. The subchannel spread packet is provided toscrambling element 22, which as described previously scrambles thepacket in accordance with the long code generated by long code generator16.

The PN scrambled packets from scrambling elements 18 and 22 are providedto complex PN spreading means 24, which performs a complex spreadingoperation as described in aforementioned U.S. patent application Ser.No. 08/856,428. The inputs I and Q are complex spread by the inputpsueudonoise sequences PN_(i) and PN_(q) to provide outputs I and Q inaccordance with the following equations:I=I′PN _(I) −Q″PN _(Q),  (1)Q=I′PN _(Q) +Q″PN _(I).  (2)

The outputs from complex PN spreading means 24 are provided to basebandfilters (BBF) 26 and 28 which provide the appropriate filtering of theresultant waveform. The filtered waveforms are provided to upconversionelements 30 and 32 and are upconverted to the carrier frequency (f_(c))in accordance with a QPSK modulation format. The two upconvertedwaveforms are summed in summing element 34, the output of which isprovided to transmitter (TMTR) 36, which amplifies and filters thesignal and provides it to antenna 38 for transmission.

FIG. 4 illustrates a first receiver system for receiving the waveformtransmitted in accordance with FIG. 1. The signal is received at antenna100 and provided to receiver (RCVR) 102, which filters and amplifies thereceived signal. The received signal is then provided to downconverters104 and 106, which downconvert the received signal in accordance with aQPSK downconversion methodology as is well known in the art. The I and Qcomponents of the downconverted signals are provided to baseband filters(BBF) 108 and 110, which filter the signals and provide the basebandsignals to complex PN despreading means 112. The implementation ofcomplex despreading means 112 is described in detail in theaforementioned U.S. patent application Ser. No. 08/856,428, nowabandoned, and removes the PN spreading that was described in equations1 and 2 above.

Again, the exemplary embodiment illustrates a method for distinguishingbetween two possible rates. One skilled in the art will understand thatthe receiver structure shown can be extended to an arbitrary number ofpotential rates by increasing the number of demodulator/decoder elements114. In the exemplary embodiment, the complex despread packet data isprovided to demodulator/decoders 114 a and 114 b. It will be understoodby one skilled in the art that the demodulation can also work with onehardware element running at a higher rate. Moreover, the receiver candescramble the pilot using the different long code masks correspondingto the different rate hypothesis and estimate the resulting energyobtained by using each hypothesis.

Demodulator/decoder 114 a demodulates the data using a long code maskassociated with the first data rate hypothesis and demodulator/decoder114 b demodulates the data using a long code mask associated with thesecond data rate. As described previously, the two long PN codescorresponding to the two rate hypotheses will be uncorrelated. Thedemodulation and decoding of the data using the correct long code mask(corresponding to the correct rate hypothesis) will demodulate anddecode correctly, while the decoding of the data using the incorrectlong code mask (corresponding to the incorrect rate hypothesis) willdemodulate and decode incorrectly. The correct demodulation anddecoding, corresponding to the correct hypothesis of the data will bedetected by CRC check and selector 140. CRC check and selector element140 will generate a set of CRC bits from the decoded data estimates andwill compare those with the decoded CRC estimates. If the generated CRCbits match the decoded CRC estimates, the data at that rate will beprovided to the user.

Turning to the details of demodulator/decoders 114, the complex PNdespread packets are provided to descrambling elements 118 and 120. Thepackets are descrambled in accordance with long PN codes generated bylong code generators 116, which generate the long codes in accordancewith a long code mask corresponding to the mobile station and a ratefrom the set of possible rates as described with respect to thetransmission process.

The descrambled data packets from descrambling elements 118 and 120 areprovided to subchannel despreading elements 122, 124, 126 and 128, whichremove the Walsh subchannel coverings from the received data stream.Subchannel despreading elements 122 and 124 remove the data subchannelcovering from the descrambled data in accordance with the datasubchannel Walsh sequence (W_(data)). Subchannel despreading elements126 and 128 remove the pilot subchannel coverings from the descrambleddata in accordance with the pilot subchannel Walsh sequence (W_(pilot)).

The output from subchannel despreading elements 126 and 128 are providedto pilot filter 132 which performs a moving average filtering operationon the signal in order to reduce the effects of noise on the receivedpilot signal. The I and Q components from pilot filter 132 are providedto dot product circuit 130 which performs a coherent demodulation of theQPSK data channel. The design of dot product elements is well known inthe art and is described in detail in U.S. Pat. No. 5,506,865, entitled“PILOT CARRIER DOT PRODUCT CIRCUIT,” which is assigned to the assigneeof the present invention and incorporated by reference herein.

The demodulated data signal out of dot product element 130 is providedto repetition combiner 134. Repetition combiner 134 combines therepeated symbols in the packet in accordance with the rate hypothesisbeing tested by the demodulation/decoder 114. Deinterleaver 136, whichreorders the symbols in accordance with a rate dependent deinterleavingformat, provides the reordered symbols. The reordered symbols areprovided to decoder 138, which decodes the symbols. In the exemplaryembodiment, decoder 138 is a turbo decoder, the implementation of whichis well known in the art and is described in detail in U.S. Pat. No.5,446,747. The present invention is equally applicable to other decoderstructures such as trellis decoders and block decoders.

The decoded data packets from demodulator/decoder 114 a and 114 b areprovided to CRC check and selector 140. In the exemplary embodiment, theCRC bits are checked and the data that passes the CRC check is output asthe data demodulated and decoded at the correct rate. The presentinvention also anticipates the use of other methods for packet selectionsuch as those involving the use of the accumulated metric fromdemodulator/decoder 138, estimates of received pilot energy followingdespreading by the different long code masks, or the use of symbol errorrate (SER), which depend on the number of symbol corrections made bydemodulator/decoder 138.

FIG. 5 illustrates a second receiver system for receiving the waveformtransmitted in accordance with FIG. 1. The signal is received at antenna200 and provided to receiver (RCVR) 202, which filters and amplifies thereceived signal. The received signal is then provided to downconverters204 and 206, which downconvert the received signal in accordance with aQPSK downconversion methodology as is well known in the art. The I and Qcomponents of the downconverted signals are provided to baseband filters(BBF) 208 and 210, which filter the signals and provide the basebandsignals to complex PN despreading means 212, which despread the signalsin accordance with pseudonoise sequences PN_(I) and PN_(Q). Theimplementation of complex PN despreading means 212 is described indetail in the aforementioned U.S. patent application Ser. No. 08/856,428and removes the PN spreading that was described in equations 1 and 2above.

Again, the exemplary embodiment illustrates a method for distinguishingbetween two possible rates. One skilled in the art will understand thatthe receiver structure shown can be extended to an arbitrary number ofpotential rates by increasing the number of demodulator elements 214. Inthe exemplary embodiment, the complex PN despread packet data isprovided to demodulators 214 a and 214 b.

Demodulator 214 a demodulates the data using a long code mask associatedwith the first data rate hypothesis and demodulator 214 b demodulatesthe data using a long code mask associated with the second data ratehypothesis. As described previously, the two long PN codes correspondingto the two rate hypotheses will be uncorrelated. The demodulation of thedata using the correct long code mask (corresponding to the correct ratehypothesis) will demodulate correctly yielding a high energy demodulatedsignal, while the decoding of the data using the incorrect long codemask (corresponding to the incorrect rate hypothesis) will demodulateincorrectly yielding low energy noise. The correct demodulation,corresponding to the correct rate hypothesis will be detected byselector 236, which will compare the energies of the two demodulateddata streams.

Selector element 236 will provide the correctly demodulated data packetto repetition combiner 238 which combines the data in accordance withthe detected rate of the received data. The combined symbols areprovided to deinterleaver 240, which reorders the symbols in accordancewith a deinterleaving format selected on the basis of the determinedrate. The reordered symbols are provided to decoder 242, which decodesthe symbols in accordance with a predetermined error correction format.In the exemplary embodiment, decoder 242 is a turbo decoder, though thepresent invention is equally applicable to other decoders such astrellis or block decoders. The decoded data packet is then output to theuser.

Turning to the details of demodulators 214, the complex PN despreadpackets are provided to descrambling elements 218 and 220. The packetsare descrambled in accordance with long PN codes generated by long codegenerators 216 which generate the long codes in accordance with a longcode mask corresponding to a rate from the set of possible rates asdescribed with respect to the transmission process.

The descrambled data packets from descrambling elements 218 and 220 areprovided to subchannel despreading elements 222, 224, 226 and 228, whichremove the Walsh subchannel coverings from the received data stream.Subchannel despreading elements 222 and 224 remove the data subchannelcovering from the descrambled data in accordance with the datasubchannel Walsh sequence (W_(data)). Subchannel despreading elements226 and 228 remove the pilot subchannel coverings from the descrambleddata in accordance with the pilot subchannel Walsh sequence (W_(pilot)).

The output from subchannel despreading elements 226 and 228 are providedto pilot filter 232, which performs a moving average filtering operationon the signal in order to reduce the effects of noise on the receivedpilot signal. The I and Q components from pilot filter 232 are providedto dot product circuit 230 which performs a coherent demodulation of theQPSK data channel. The design of dot product elements is well known inthe art and is described in detail in U.S. Pat. No. 5,506,865, entitled“PILOT CARRIER DOT PRODUCT CIRCUIT,” which is assigned to the assigneeof the present invention and incorporated by reference herein.

The demodulated data signal out of dot product element 230 is providedto energy calculator 234 and to selector 236. Energy calculator 234computes the energy of the demodulated packet and provides the energyvalue to selector 236. Selector 236 selects the demodulated packet withthe greatest amount of energy. The selected packet is provided torepetition combiner 238, which combines the redundant symbol energiesand provides the combined energies to deinterleaver 240. Deinterleaver240 reorders the combined symbol energies and provides them to decoder242. Decoder 242 decodes the data and provides it to the user.

FIG. 6 illustrates a transmission system for the second exemplaryembodiment of the present invention. In the second embodiment of thepresent invention, each data packet is transmitted with a preambleindicating the data rate of the transmitted packet. The data packet isprovided to CRC and tail bit generator 300. CRC and tail bit generator300 generates a set of redundant check bits and appends those check bitsalong with a set of tail bits to the packet.

The packet output by CRC and tail bit generator 300 is provided toencoder 302, which performs a forward error coding on the packet. In theexemplary embodiment, encoder 302 is a turbo encoder. The encodedsymbols are provided to interleaver 304, which reorders the symbols inaccordance with a predetermined interleaving format. The reorderedsymbols are provided to repetition generator 306. which generates a setof redundant symbols to output a packet of a fixed number of symbolsregardless of the data rate of the packet.

The packet from repetition generator 306 is provided to gain adjustmentmeans 308, which adjusts the gain of the packet based on the data rateof the packet, and the E_(b)/N₀ required for proper transmission of thereverse link signal. The gain adjusted packet is provided to multiplexer312. In the exemplary embodiment, multiplexer 312 performs a simpleswitching operation that punctures a rate indication preamble into thedata packet by overwriting a first portion of the frame. The overwrittendata could be recovered by means of the forward correction decoder atthe receiver. In an alternative embodiment, the packet length could beadjusted so that none of the data would require to be overwritten by thepreamble.

In the current embodiment of the present invention, the set of rateindication preambles are of lengths that vary in accordance with thedata rate of the packet to be transmitted. In the exemplary embodiment,the lower the data rate of the packet, the longer will be the preambleincluded with the packet. In the exemplary embodiment, the set ofpossible rates differ from one another by factors of two, for example9.6 Kbps, 19.2 Kbps, 38.4 Kbps and 76.8 Kbps. In the exemplaryembodiment, the length of the preamble varies in inverse proportion withthe data rate of the packet. In this way, the proportion of the data inthe packet that is overwritten by the preamble remains constant due tothe variable duration of the packets to be transmitted as a function ofthe data rate.

Turning to FIGS. 7A-7D, an exemplary set of four preambles isillustrated. In the exemplary embodiment, FIG. 7A illustrates theproposed preamble for the highest possible rate in the rate set (i.e.76.8 Kbps). FIG. 7B illustrates the proposed preamble for the secondhighest possible rate in the rate set (i.e. 36.4 Kbps). FIG. 7Cillustrates the proposed preamble for the third highest possible rate inthe rate set (i.e. 19.2 Kbps). FIG. 7D illustrates the proposed preamblefor the lowest possible rate in the rate set (i.e. 9.6 Kbps).

The important characteristic to be observed regarding the proposedpreamble structure is that the preamble sequences are orthogonal overselected time periods. For example, the preamble sequence illustrated inFIG. 7A is orthogonal to preamble sequences illustrated in FIGS. 7B, 7Cand 7D over the period of its duration (0 to 4 T). Similarly, thepreamble sequence illustrated in FIG. 7B is orthogonal to the preamblesequences illustrated in FIGS. 7C and 7D over the period of its duration(0-8 T). Lastly, the preamble sequence illustrated in FIG. 7C isorthogonal to the preamble sequence illustrated in FIG. 7D over theperiod of its duration (0-16 T). The benefit of the orthogonality of thepreamble waveforms is realized at the receiver, by making detection ofthe preamble more accurate, because the correlation between twoorthogonal sequences is zero. Thus, by passing the preamble sequencethrough a correlator, such as a matched filter, will yield zero energyfor all preamble rate hypotheses except the correct preamble ratehypothesis. FIGS. 7E-7H illustrate an alternative set of proposedpreamble waveforms which manifest the same orthogonal properties asthose illustrated in 7A-7D.

Referring back to FIG. 6, the data packet is provided to subchannelspreading element 310 which covers the packet in accordance with theWalsh sequence W_(data). In addition, the rate indication signal isWalsh covered by subchannel spreading element 311. The data signal andthe preamble signal are combined by multiplexer 312. In an alternativeembodiment, the data packet could be combined with the preamble prior toperforming the Walsh covering operation. The combined Walsh coveredpacket is then provided to scrambling means 314, which scrambles thepacket in accordance with a long code sequence provided by long codegenerator and mask 316. The long code is uniquely assigned to the remotestation and used to distinguish the transmission of different remotestations simultaneously communicating with a given base station.

In the modulation of the pilot signal, a set of predetermined pilotsymbols are provided to Walsh covering means 318. In the exemplaryembodiment, the pilot symbol sequence is a string of all zeroes. Walshcovering means 318 covers the pilot symbols in accordance with the Walshsequence W_(pilot). The Walsh covered pilot symbols are provided tospreading means 320 which scrambles the Walsh covered pilot symbols inaccordance with a long PN sequence from long code generator and mask316. The outputs from scramblers 314 and 320 are input to complex PNspreading element 322 along with pseudonoise sequences PN_(I) andPN_(Q). Complex PN spreading element 322 performs a complex PN spreadingon the input signal in accordance with equations 1 and 2 above.

The I and Q channel outputs from the complex PN spreading element 322are provided to baseband filters (BBFs) 324 and 326. Baseband filters324 and 326 filter the baseband signals and provide the filtered signalsto upconverters 328 and 330. Upconverters 328 and 330 upconvert thesignals, in accordance with a QPSK modulation format wherein theresulting upconverted signals are 90 degrees out of phase with oneanother. The upconverted signals are summed in summing element 332 andprovided to transmitter (TMTR) 334 where the signal is amplified andfiltered and transmitted through antenna 336.

FIG. 8 illustrates the receiver system of the second embodiment. Thesignal is received at antenna 400 and provided to receiver (RCVR) 402,which filters and amplifies the received signal. The received signal isthen provided to downconverters 404 and 406, which downconvert thereceived signal in accordance with a QPSK downconversion methodology asis well known in the art. The I and Q components of the downconvertedsignals are provided to baseband filters (BBF) 408 and 410, which filterthe signals and provide the baseband signals to complex PN despreadingelement 412. The implementation of complex PN despreading element 412 isdescribed in detail in the aforementioned U.S. patent application Ser.No. 08/856,428, now abandoned, and removes the complex PN spreading thatwas described in equations 1 and 2 above.

The despread I and Q signals are provided descrambling elements 416 and418. Descrambling elements 416 and 418 descramble the signals inaccordance with a long code provided by long code and mask generator414. The descrambled I and Q signals are provided by descramblingelements 416 and 418 to subchannel despreading elements 426, 428, 430and 432, which remove the Walsh subchannel coverings from the receivedsignals. Subchannel despreading elements 426 and 428 remove the datasubchannel covering from the descrambled data in accordance with thedata subchannel Walsh sequence (W_(data)). Subchannel despreadingelements 430 and 432 remove the pilot subchannel coverings from thedescrambled data in accordance with the pilot subchannel Walsh sequence(W_(pilot)).

The output from subchannel despreading elements 430 and 432 are providedto pilot filter 434 which performs a moving average filtering operationon the signal in order to reduce the effects of noise on the receivedpilot signal. The I and Q components from pilot filter 434 are providedto dot product circuit 436 which performs a coherent demodulation of theQPSK data channel. The design of dot product elements is well known inthe art and is described in detail in U.S. Pat. No. 5,506,865, entitled“PILOT CARRIER DOT PRODUCT CIRCUIT,” which is assigned to the assigneeof the present invention and incorporated by reference herein.

The demodulated data signal out of dot product element 436 is providedto demultiplexer (De-Mux) 420. Demultiplexer 420 outputs the datainitially to preamble detector 424. Preamble detector 424 determines therate indicated by the despread preamble. Many implementations ofpreamble detectors are possible. For example, preamble detector 424 canbe implemented using a bank of matched filters or other correlators.Upon finding a preamble with sufficient correlation energy to one of thepredetermined set of preambles, the rate is declared as having beensuccessfully detected. In an alternative embodiment, the preamble couldbe detected noncoherently, in which case the despread data would beprovided directly to the preamble detector through demultiplexer 420from subchannel despreading elements 426 and 428.

Upon successful detection of one of the candidate preambles, preambledetector 424 sends a signal indicative of the detected rate torepetition combiner 438, deinterleaver 440 and decoder 442, whichperform their operations in accordance with this information. Inaddition, upon detection of the end of the preamble message, preambledetector sends a signal indicating the detection of the end of thepreamble to demultiplexer 420, in response to which demultiplexer 420begins to output the despread data to repetition combiner 438.

Repetition combiner 438 combines the repeated symbol energies in thepacket in accordance with the detected rate of the received packet. Thecombined symbol energies are provided to deinterleaver 440, whichreorders the symbol energies in accordance with a deinterleaving formatselected in accordance with the rate signal from preamble detector 424.The reordered symbols are provided to decoder 442 which decodes thesymbols. In the exemplary embodiment, decoder 442 is a turbo decoder,the implementation of which is well known in the art and is described indetail in U.S. Pat. No. 5,446,747. The present invention is equallyapplicable to other decoder structures such as trellis decoders andblock decoders. The decoded data estimates are output by decoder 442 tothe user.

FIG. 9 illustrates the preferred embodiment of the present invention fortransmitting variable rate data. In the preferred embodiment, packets atdifferent data rates contain a different number of information bits butspan the same duration of time (i.e. 2 frames=32 slots=53 msec). Thedata transmission system again transmits a control channel distinct froma data channel. In the third embodiment of the present invention, thecontrol channel includes three types of information, which are timemultiplexed together. The first type of information provided on thecontrol channel is the pilot signal. The second is a rate indicationmessage that indicates the rate of the data packet being transmittedconcurrently with the control channel information. The third is a raterequest message which is the request by the remote station for a servingbase station to provide data up to that rate.

In the preferred embodiment, the rate request information provides anindication both of the rate at which the remote station desires data tobe downloaded to it, and also the base station or base station sectorwhich the remote station wishes to perform the data transmission. In thepreferred embodiment, the indication of which base station or sector ofa predetermined set of base stations or sectors is based on a spreadingfunction that will only be properly decoded by the base station soughtto transmit to the remote station.

In identifying the Walsh function, the superscript identifies the orderof the Walsh function, and the subscript identifies the index of theWalsh function of that order. Tables 1-3 below provide the Walshfunction used in the current description. TABLE 1 W₀ ² 00 W₁ ² 00

TABLE 2 W₀ ⁴ 0000 W₁ ⁴ 0101 W₂ ⁴ 0011 W₃ ⁴ 0110

TABLE 3 W₀ ⁸ 0000 0000 W₁ ⁸ 0101 0101 W₂ ⁸ 0011 0011 W₃ ⁸ 0110 0110 W₄ ⁸0000 1111 W₅ ⁸ 0101 1010 W₆ ⁸ 0011 1100 W₇ ⁸ 0110 1001

As in the previous two embodiments, the pilot channel symbols are asimple predetermined sequence. In the exemplary embodiment, the pilotsymbols are a string of all zeroes, which are provided to multiplexer(MUX) 500. In the exemplary embodiment, the rate indication signal is abiorthogonal waveform. Thus, the input to Walsh covering element 502 isa binary value, the switching of which will result in the inversion ofthe resultant waveform. The symbols from Walsh covering element 502 areprovided to Walsh covering element 504, which provides a second Walshcovering of the data, in which the index of the Walsh cover usedprovides the second portion of the rate indication value. In theexemplary embodiment, the second Walsh covering can take on eightdifferent forms, which in combination with the input bit allows for thespecification of up to 16 different rates. The Walsh symbols from Walshcovering element 504 are provided to multiplexer 500. In the exemplaryembodiment, the rate indication is punctured into the pilot symbols onceevery slot for 32 consecutive slots (2 frames) spanned by a reverse linkpacket. This is to provide time diversity in a fading environment.

Turning to the rate request message, the exemplary embodiment providesfor the specification of up to 16 possible forward link (from the basestation to the remote station) data rates. A 4-bit index is provided toblock encoder 506. In the exemplary embodiment, block encoder 506 mapsthe 4-bit input into a set of 8 possible Walsh symbols or their inverseusing a (8,4,4) block code, the design and implementation of which arewell known in the art. The block encoded rate request is then providedto repetition generator 508, which provides redundancy for the purposesof time diversity to protect against burst errors. The rate requestmessage is then provided to gain adjustment element 510, which adjuststhe gain to provide for proper reception of the rate request message.The gain adjusted signal is provided to Walsh covering element 512,which provides additional redundancy into the rate request message.

The Walsh covered message from Walsh covering element 512 is thenprovided to Walsh covering element 514. The purpose of Walsh coveringelement 514 is to indicate the best base station or base station sectorfrom which to receive forward link data. In the exemplary embodiment,the remote station measures the C/I of transmissions from a set of basestations from which it is capable of receiving data. The base station,which can provide data to the remote station at the highest C/I, isselected by the remote station to download data to the remote station.The selected base station is indicated by using a Walsh sequence thatwill only be properly demodulated by the selected base station. All basestations and sectors in the remote stations active set (or set of basestation/sectors capable of transmission to the remote station) willattempt to demodulate the signal using an assigned W_(i) ⁸ sequence.However, only the selected base station will correctly demodulate therequest and will transmit to the remote station. The encoded raterequest information, the rate indication, and the pilot data are timemultiplexed together by multiplexer 500. The multiplexed control signalis provided to subchannel spreading element 516, which covers theresulting signal with a Walsh covering that is orthogonal to that usedto cover the data subchannel.

On the data subchannel, variable rate data packets are provided to CRCand tail bit generator 518. CRC and tail bit generator 518 generates aset of redundant check bits and append those check bits along with a setof tail bits to the packet.

The packet output by CRC and tail bit generator 518 is provided toencoder 520, which performs a forward error coding on the variable ratedata packet. In the exemplary embodiment, encoder 520 is a turboencoder. The encoded symbols are then provided to interleaver 522, whichreorders the symbols in accordance with a predetermined interleavingformat. The reordered symbols are then provided to repetition generator524, which generates a set of redundant symbols to output a packetcontaining a fixed number of symbols regardless of the data rate of thepacket.

The packet from repetition generator 524 is provided to gain adjustmentmeans 526 which adjusts the gain of the packet based on the data rate ofthe packet and the E_(b)/N₀ required for proper transmission of thereverse link signal. The gain adjusted packet is provided to subchannelspreading element 528, which covers the packet with a Walsh sequencethat is orthogonal to the Walsh sequence used to cover the controlpacket.

The data packet and the control packet are provided to scrambling means534 and 532, respectively. Scrambling elements 532 and 534 scramble thepackets in accordance with a long code sequence provided by long codegenerator and mask 530. The outputs from scrambling elements 532 and 534are input to complex PN spreading element 536 along with pseudonoisesequences PN_(I) and PN_(Q). Complex PN spreading element 536 performs acomplex PN spreading on the input signal in accordance with equations 1and 2 above.

The I and Q channel outputs from the complex PN spreading element 536are provided to baseband filters (BBFs) 538 and 540. Baseband filters538 and 540 filter the baseband signals and provide the filtered signalsto upconverters 542 and 544. Upconverters 542 and 544 upconvert thesignals, in accordance with a QPSK modulation format wherein theresulting upconverted signals are 90 degrees out of phase with oneanother. The upconverted signals are summed in summing element 546 andprovided to transmitter (TMTR) 548 where the signal is amplified andfiltered and provided through duplexer 549 for transmission throughantenna 550.

In addition, remote station 554 includes a variable rate receivesubsystem 552 for receiving forward link variable rate data from a basestation or plurality of base stations capable of transmitting to remotestation 554. The forward link variable rate data is received throughantenna 550 and provided through duplexer 549 to variable rate receivesubsystem 552.

FIG. 10 illustrates an exemplary embodiment of the receiver for thethird embodiment. The signal is received at antenna 600 and provided toreceiver (RCVR) 602, which filters and amplifies the received signal.The received signal is then provided to downconverters 604 and 606,which downconvert the received signal in accordance with a QPSKdownconversion methodology as is well known in the art. The I and Qcomponents of the downconverted signals are provided to baseband filters(BBF) 608 and 610, which filter the signals and provide the basebandsignals to complex PN despreading element 612. The implementation ofcomplex PN despreading element 612, which removes the complex PNspreading, was described in equations 1 and 2. An implementation ofcomplex PN despreading element 612 is described in detail in theaforementioned U.S. patent application Ser. No. 08/856,428, nowabandoned.

The complex PN despread packets are provided to descramblers 614 and618. The packets are descrambled in accordance with long PN codesgenerated by long code and mask generators 618 which generate the longcode sequence as described above with respect to previous embodiments.

The descrambled data packets from descramblers 614 and 616 are providedto subchannel despreading elements 620, 622, 624 and 626, which removethe Walsh subchannel coverings from the received data stream. Subchanneldespreading elements 620 and 622 remove the data subchannel coveringfrom the descrambled data in accordance with the pilot subchannel Walshsequence (W₂ ⁴). Subchannel despreading elements 624 and 626 remove thedata subchannel coverings from the descrambled data in accordance withthe pilot subchannel Walsh sequence (W₀ ⁴).

The output from subchannel despreaders elements 624 and 626 are providedto demultiplexer (De-Mux) 628. Demultiplexer 628 separates out thedifferent portions of the received control channel corresponding to thepilot symbols, the rate indication symbols, and the data requestsymbols, and outputs that data to three separate outputs.

The pilot symbols provided by demultiplexer 628 onto a first output areprovided to pilot filter 632 which performs a moving average filteringoperation on the signal in order to reduce the effects of noise on thereceived pilot signal. The I and Q components from pilot filter 632 areprovided to dot product circuit 630 which performs a coherentdemodulation of the QPSK data channel. The design of dot productelements is well known in the art and is described in detail in U.S.Pat. No. 5,506,865, entitled “PILOT CARRIER DOT PRODUCT CIRCUIT,” whichis assigned to the assignee of the present invention and incorporated byreference herein.

The demodulated data signal out of dot product element 630 is providedto repetition combiner 638. Repetition combiner 638 combines therepeated symbols in the packet in accordance with the detected reverselink rate signal provided by rate indication decoder 634. The combinedsymbol energies are provided to deinterleaver 640 which reorders thesymbols in accordance with the detected rate indication signal providedby rate indication decoder 634. The reordered symbols are provided todecoder 642 which decodes the symbols in accordance with the detectedrate indication signal. In the exemplary embodiment, decoder 642 is aturbo decoder, the implementation of which is well known in the art andis described in detail in U.S. Pat. No. 5,446,747. The present inventionis equally applicable to other decoder structures such as trellisdecoders and block decoders.

Demultiplexer 628 provides the received symbol energies corresponding tothe rate indication signal on a second output to rate indication decoder634. Rate indication decoder 634 can be implemented in a variety of wayssuch as by using a bank of correlators to correlate the received symbolenergies with the possible rate indication waveforms. The waveform thathas the highest correlation energy would be detected as the transmittedwaveform, thus determining the rate indication value. The rateindication value is provided to repetition combiner 638, deinterleaver640 and decoder 642 to assist in the operation of those elements.

Demultiplexer 628 provides the received symbol energies corresponding tothe rate request message signal on a third output to rate request (DRQ)decoder 636. Each base station in the active set of the remote stationwould attempt to decode the rate request message using an assigned Walshsequence. Only the base station that the remote station desires totransmit the data will be able to correctly decode the rate requestmessage. After the selected base station or sector removes the Walshcovering from the rate request message, the message is block decoded toprovide the requested rate information to the base station. Thisinformation is provided to a control processor in the selected basestations or sector which schedules data transmissions to the remotestation in accordance with this rate request.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein, but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

1. An apparatus for transmitting a variable rate user data packet,comprising: data coding means for encoding and spreading the variablerate user data packet to produce a Walsh covered encoded variable rateuser data packet; wherein the spreading is in accordance with a firstWalsh code; rate indication coding means for encoding a rate indicationdata, wherein the rate indication data indicates the transmission rateof the variable rate user data packet, to produce an encoded rateindication data; wherein the data coding means produces the Walshcovered encoded variable rate user data packet in accordance with a ratebeing indicated by the rate indication data; multiplexer means forcombining the encoded rate indication data and pilot data to produce acontrol data packet; means for spreading the control data packet inaccordance with a second Walsh code to produce a Walsh covered controldata packet; wherein the first Walsh code and the second Walsh code areorthogonal to each other; means for scrambling the Walsh covered controldata packet and the Walsh covered encoded variable rate user data packetin accordance with a code sequence; and means for concurrentlytransmitting the scrambled Walsh covered control data packet and thescrambled Walsh covered encoded variable rate user data packet.
 2. Theapparatus of claim 1 wherein the transmission of the encoded rateindication data spans over duration of a time frame.
 3. The apparatus ofclaim 2 wherein the encoded rate indication data is punctured into thepilot data at least once in every time slot of the time frame.
 4. Amethod for transmitting a variable rate user data packet comprising:encoding and spreading the variable rate user data packet to produce aWalsh covered encoded variable rate user data packet; wherein thespreading is in accordance with a first Walsh code; encoding a rateindication data, wherein the rate indication data indicates thetransmission rate of the variable rate user data packet, to produce anencoded rate indication data; wherein the Walsh covered encoded variablerate user data packet is produced in accordance with a rate beingindicated by the rate indication data; multiplexing to combine theencoded rate indication data and pilot data to produce a control datapacket; spreading the control data packet in accordance with a secondWalsh code to produce a Walsh covered control data packet; wherein thefirst Walsh code and the second Walsh code are orthogonal to each other;scrambling the Walsh covered control data packet and the Walsh coveredencoded variable rate user data packet in accordance with a codesequence; and concurrently transmitting the scrambled Walsh coveredcontrol data packet and the scrambled Walsh covered encoded variablerate user data packet.
 5. The method of claim 4 wherein the transmissionof the encoded rate indication data spans over duration of a time frame.6. The method of claim 5 wherein the encoded rate indication data ispunctured into the pilot data at least once in every time slot of thetime frame.
 7. An apparatus for receiving a variable rate user datapacket transmission, comprising: means for concurrently receiving ascrambled Walsh covered control data packet and a scrambled Walshcovered encoded variable rate user data packet; means for de-scramblingthe received scrambled Walsh covered control data packet and thereceived scrambled Walsh covered encoded variable rate user data packetin accordance with a code sequence; means for de-spreading thede-scrambled control data packet in accordance with a control channelWalsh code to produce a control data packet; means for de-multiplexingthe de-spreaded control data packet to produce received encoded rateindication data and received pilot data; means for decoding the receivedencoded rate indication data to produce a rate indication data, whereinthe rate indication data indicates the transmission rate of the variablerate user data packet, means for decoding and de-spreading thede-scrambled Walsh covered encoded variable rate user data packet toproduce the variable rate user data packet in accordance with a datachannel Walsh code, the rate being indicated by the rate indication dataand the received pilot data; wherein the control channel Walsh code andthe data channel Walsh code are orthogonal to each other.
 8. Theapparatus of claim 7 wherein the reception of the encoded rateindication data spans over duration of a time frame.
 9. The apparatus ofclaim 8 wherein the encoded rate indication data is punctured into thepilot data at least once in every time slot of the time frame.
 10. Amethod for receiving a variable rate user data packet transmission,comprising: concurrently receiving a scrambled Walsh covered controldata packet and a scrambled Walsh covered encoded variable rate userdata packet; de-scrambling the received scrambled Walsh covered controldata packet and the received scrambled Walsh covered encoded variablerate user data packet in accordance with a code sequence; de-spreadingthe de-scrambled control data packet in accordance with a controlchannel Walsh code to produce a control data packet; de-multiplexing thede-spreaded control data packet to produce received encoded rateindication data and received pilot data; decoding the received encodedrate indication data to produce a rate indication data, wherein the rateindication data indicates the transmission rate of the variable rateuser data packet, decoding and de-spreading the de-scrambled Walshcovered encoded variable rate user data packet to produce the variablerate user data packet in accordance with a data channel Walsh code, therate being indicated by the rate indication data and the received pilotdata; wherein the control channel Walsh code and the data channel Walshcode are orthogonal to each other.
 11. The method of claim 10 whereinthe reception of the encoded rate indication data spans over duration ofa time frame.
 12. The method of claim 11 wherein the encoded rateindication data is punctured into the pilot data at least once in everytime slot of the time frame.